As Boston approaches its cap on charter schools seats, and long wait lists remain at many of the Commonwealth charter schools serving Boston residents, efforts have begun to lift the charter cap and expand the number of seats available to Boston residents. This situation raises questions about whether the increase in charter seats is the reason for the annual budget problems facing the Boston Public Schools (BPS). Is the growth in charter school seats taking state Chapter 70 school aid away from the BPS schools? How is Chapter 70 education aid allocated to cities and towns and charter schools? Do Commonwealth charter schools receive an unfair share of public resources for education? The purpose of this report is to answer these questions and more by explaining the structure of educational aid in Boston and analyzing the effect that charter seat expansion, and the resulting increased cost of the charter school assessment has had on the City and the operations of the BPS. The number of Boston resident students attending Commonwealth charter schools is currently 9,260 or 14% of all Boston resident students attending a public school. In this report, "charter schools" refer to Commonwealth public charter schools. Also, all fiscal 2016 financial information is budgeted not actuals.